It is known that a patrol of aircraft, for example of fighters or military transporters, is composed of a lead aircraft, also called the leader, which is followed in flight according to a particular spacing (defined vertically, longitudinally and laterally) by one or more follower aircraft, also called wingmen. The relative flight between the lead aircraft and a follower aircraft may be performed:                either simply (and exclusively) on the basis of the judgement of the pilot of the follower aircraft, as a function of his direct vision of the lead aircraft;        or by way of a system of information and/or of piloting aid, such as an electronic system for aiding patrol flight comprising an automatic piloting means.        
In this second case, the automatic piloting means automatically guides the follower aircraft in such a way as to maintain its prescribed position within the patrol. The engagement of such a means of automatic piloting of the follower aircraft is tied to the satisfaction of a plurality of engagement conditions which usually depend on the heading of the lead and follower aircraft and on the relative positions (lateral and longitudinal) between these lead and follower aircraft. Said automatic piloting means (of the electronic system for aiding patrol flight) can therefore be engaged only if the aforesaid engagement conditions are satisfied. If such is not the case, the pilot must bring the follower aircraft into a situation (relating for example to its speed and/or its heading) making it possible to satisfy said engagement conditions. However, the criteria used in these engagement conditions are not intuitively identifiable by the members of the crew and in particular by the pilot. So, to know whether he can engage the automatic piloting means at a current instant, the pilot of the follower aircraft must rely solely on his knowledge of these criteria and on their abstract visualization which is generally carried out on a standard display (of the system for aiding patrol flight). This greatly increases the work load of the pilot of the follower aircraft in this situation.